COVID has suddenly made them a big deal here in Spain though. QR codes are everywhere now. Restaurants and bars aren't supposed to pass menus around for hygiene reasons, so those are now all QR codes on every table. Gyms and swimming pools etc now must require reservations for entry to control numbers, so those are all managed with emailed QR codes you scan at the door. You need a completed health form to enter the country, and you have to prove it at the border by scanning a QR code from the form.
They've gone right the way from niche gimmick to day-to-day necessity at incredible speed. En route this has improved lots of things too - e.g. quite a few bars & fast food restaurants let you order and pay directly from the menu behind their QR code, and there's far fewer annoying paper forms anywhere. I don't see them going away.